Add the concept of QueueEnabledVoters to blink scheduler TaskQueue

third_party/WebKit/public/platform/scheduler/base/task_queue.h

Index: third_party/WebKit/public/platform/scheduler/base/task_queue.h
diff --git a/third_party/WebKit/public/platform/scheduler/base/task_queue.h b/third_party/WebKit/public/platform/scheduler/base/task_queue.h
index ac36e75926a4782d0284fa312d650b15bae76e80..815645cca187648a63c8620e214e9997b28c358b 100644
--- a/third_party/WebKit/public/platform/scheduler/base/task_queue.h
+++ b/third_party/WebKit/public/platform/scheduler/base/task_queue.h
@@ -117,9 +117,32 @@ class BLINK_PLATFORM_EXPORT TaskQueue : public base::SingleThreadTaskRunner {
     bool should_report_when_execution_blocked;
   };
 
-  // Enable or disable task execution for this queue. NOTE this must be called
-  // on the thread this TaskQueue was created by.
-  virtual void SetQueueEnabled(bool enabled) = 0;
+  // An interface that lets the owner vote on whether or not the associated
+  // TaskQueue should be enabled.
+  class QueueEnabledVoter {

[Sami, 2016/11/29 14:45:17]

I think "voter" works but just to throw another (somewhat stl-inspired) idea out
there: SharedEnableState

[alex clarke (OOO till 29th), 2016/11/29 16:49:11]

Acknowledged.

+   public:
+    QueueEnabledVoter() {}
+    virtual ~QueueEnabledVoter() {}
+
+    // Votes to enable or disable the associated TaskQueue. The TaskQueue will
+    // only be enabled if all the voters agree it should be enabled, or if there
+    // are no voters.
+    // NOTE this must be called on the thread the associated TaskQueue was
+    // created on.
+    virtual void SetQueueEnabled(bool enabled) = 0;
+
+    // Returns the TaskQueue this voter votes on.
+    virtual TaskQueue* GetTaskQueue() const = 0;

[Sami, 2016/11/29 14:45:17]

GetTaskQueueForTest? Doesn't seem like we need this for anything else.
(Alternatively we could cast to the Impl class in the test and get the queue
from there)

[alex clarke (OOO till 29th), 2016/11/29 16:49:11]

Done.

+
+   private:
+    DISALLOW_COPY_AND_ASSIGN(QueueEnabledVoter);
+  };
+
+  // Returns an interface that allows the caller to vote on whether or not this
+  // TaskQueue is enabled. The TaskQueue will be enabled if there are no voters
+  // or of all agree it should be enabled.

[Sami, 2016/11/29 14:45:17]

s/of/if/

[alex clarke (OOO till 29th), 2016/11/29 16:49:11]

Done.

+  // NOTE this must be called on the thread this TaskQueue was created by.
+  virtual std::unique_ptr<QueueEnabledVoter> GetQueueEnabledVoter() = 0;
 
   // NOTE this must be called on the thread this TaskQueue was created by.
   virtual bool IsQueueEnabled() const = 0;